Theoretical Study of the Photoabsorption Spectrum of Na<sub>8</sub>, Na<sub>20</sub>, Cs<sub>8</sub> and Cs<sub>1O</sub>0 Clusters

Physical Review B 45, 13657 - 13663 (1992)

Theoretical Study of the Photoabsorption Spectrum of Na8, Na20, Cs8 and Cs1O0 Clusters

A. Rubio, L.C. Balbás, J.A. Alonso

We have used the spherically-averaged-pseudopotential model to study, within the time-dependent density-functional theory, the response to light Na8, Na20, Cs8 and Cs1O0 clusters. The influence of electronic and geometrical effects has been analyzed by comparing our results to experiment and with other available calculations. From this analysis we conclude (1) the position of the surface plasmon in the photoabsorption spectrum depends mainly on the cluster size; (2) the two-peak structure of the photoabsorption spectrum of Na20, Cs8, and Cs10O originates from the coupling of the collective mode (surface plasmon) with a particle-hole transition; (3) in the cases of Cs8 and Cs10O the geometries which lead to agreement with experiment are such that Cs atoms are absent from the cluster center; and (4) the particle-hole transition responsible for the plasmon fragmentation in Cs10O involves a p-type electronic level with partial oxygen character, contrary to the picture of treating Cs10O as a system with only eight active electrons.

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